#109 Prop to set visibleCount number of lines in virtual mode

[LukeFinch]

PR Related to issue #109

This adds 2 props to the tree. virtualLines and autoHeight
Virtual lines sets the number of items in the virtual list. Auto Height will set the height of the virtual list container, based on the number of items.

This does however mean that if a user doesn't get autoHeight, they must style the container to have a height.

I have also updated the VirtualList.vue example, so show the new props.

[leezng]

@LukeFinch
I'm sorry to find some problems, after running your modification:

• When I turn off autoHeight, there will be a large area of blank space in the virtual list of the page.
• When I change the virtualLines to 20, and then scroll to the 20th line or so in the list, the component is rendered as blank.

The above problems can be found on the example page.

[LukeFinch]

Thanks, I'll investigate.

With regards to autoHeight, it would require the user to set a height, using a css property if they set the prop to false.
Do you have a preferred method for implementing such a thing? Or would you recommend removing the autoHeight prop?

Investigating the other issue, it looks to be changing the translateY of state, and I'm guessing that the issue occurs when you change the virtualLines prop after it has mounted. The translateY jumps from 980 to 990000 when scrolling past a certain point.

[leezng]

I think it needs to be split into 2 PRs to ensure that each PR corresponds to an independent demand and is easy to trace.

Can you help split it? The current PR is only to add virtualLines prop.

[LukeFinch]

Just pushed changes removing auto height.

The issue still persists when changing the number of lines after the component has mounted.
Do you think this could be fixed with a watch effect? Re-render the component if the number of lines changes?

[leezng]

This is a problem caused by the data type, I have fixed it. 8a4aa3f